We are currently investigating the following in baboons: 1) Assessment of the effectiveness of synchronized pulsatile coronary sinus retroperfusion. 2) Determining the relationship between acute epicardial ST segment mapping after ligation of a coronary artery and the perfusion bed of that artery. Also, the relationship between chronic histologically determined infarct size and the perfusion bed of that occluded coronary artery will be studied. 3) Comparison of the dog and baboon as models for use in assessing therapeutic interventions aimed at reducing infarct size. 4) Assessment of pretreatment with aspirin on ultimate infarct size. 5) Observing the changes in myocardial intracellular potentials throughout a region of ischemia.